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Seawater Sensors

Temperature, Salinity, and Conductivity

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ShoreStation Seawater Observations
Seawater Temperature (deg F) 57.1
Seawater Temperature (deg C) 14.0
Seawater Salinity (PSU) 33.700
Seawater Density (sigma-t kg/m3-1000) 25.190
Seawater Conductivity (S/m) 4.0506
Last update: Sat Jun 24 06:50:00 2017 PDT

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Seawater Conductivity

Conductivity is the measure of a material’s ability to conduct an electric current. In ocean sciences, the electrical conductivity of seawater is used as an indication of salinity. The saltier the water, the higher the conductivity will be. Seawater salinity can be calculated from measured values of conductivity and temperature.

Seawater Salinity

Salinity refers to the amount of salts dissolved in water, expressed as parts per thousand, or ppt. This corresponds to the amount of salt in grams dissolved in 1000 grams of water. However, salinity is difficult to measure directly and is generally calculated from conductivity and temperature measurements. The current accepted standard is the 1978 Practical Salinity Scale Equations and its units are Practical Salinity Units, or PSU.

Generally, salinity increases with depth. Water with higher salinity levels is denser and descends, causing a layering or stratified affect in the deeper water. At the surface, salinity is influenced by various factors, including fresh water input and evaporation. Precipitation and run off from streams and rivers cause decreased salinity levels, while heat and wind cause evaporation that tends to increase salinity levels. The area of distinct change between this dynamic surface layer and the deeper ocean is known as a halocline.

Researchers are interested in the impact salinity levels have on marine organisms. The life cycle and diversity of marine organisms in an area is dependent on the seawater characteristics. The effect of salinity is particularly noticeable in bays, estuaries and nearshore coastal areas with high salinity gradients.

Seawater Temperature

The temperature of seawater changes very gradually and its stability plays an important role in moderating global climate. Ocean current patterns move the heated water from the equator up toward the poles and move the cold polar water toward the equator thus moderating the seawater temperature.

Seawater temperature generally decreases with depth. Colder water is denser and sinks, causing a layering or stratified affect in the deeper water. However, at the surface, the degree of stratification is influenced by factors including wind and tides. The area of distinct change between this dynamic surface layer and the deeper ocean is known as a thermocline.

In some coastal regions such as California, high winds cause upwelling. Strong seasonal winds drive warmer surface waters away from the coast, and this divergence draws the cold, nutrient rich water up from beneath the thermocline to the surface. Upwelling regions generally feature high productivity and therefore are of economic significance. Researchers may look at the impact of seawater temperature on marine organisms, and use seawater temperature and wind measurements to study upwelling and climate change.

BML Seawater Salinity BML Seawater Conductivity BML Seawater Temperature BML Seawater Temperature BML Seawater Density

 

Instrument Type: Sea-Bird Electronics SBE 16+ SEACAT

BML seawater sensor sbe45Description: Self contained conductivity and temperature sensor, with strain gauge pressure sensor. Pumped during sampling with SBE 5T submersible pump.

Location: Water sampled in sump at Laboratory seawater intake, in the pumphouse at the shore of Horseshoe Cove.
Latitude 38° 18’ 58.2” N
Longitude 123° 04’ 10.2” W

Installed: 21 March 2003

Specifications: Temperature
Range: -5 to +35 °C
Resolution: 0.0001 °C
Accuracy: 0.005 °C

Specifications: Conductivity
Range: 0 to 9 S/m
Resolution: 0.00005 S/m
Accuracy: 0.0005 S/m

Specifications: Pressure
Range: 0 to 44 m
Resolution: 0.002 % of full scale range
Accuracy: 0.1% of full scale range

Acquisition Settings:
Sample interval = 5 minutes
Measurements per sample = 20 (averaged)
Pumped during sample

Instrument Type: Sea-Bird Electronics SBE 45 MicroTSG Thermosalinograph

sbe45Description:
An ultra-precision Wein Bridge oscillator to generate a frequency output in response to changes in conductivity and a bridge circuit using an ultra-stable aged thermistor and Vishay precision reference resistor for seawater temperature

Location: Water sampled at Laboratory seawater intake
Latitude 38° 18' 59.46" N
Longitude 123° 04' 15.34" W

Installed: 1 January 2001 - March 2003

Specifications: Temperature:
Range: -5 to +35 °C
Resolution: 0.0001 °C
Accuracy: 0.002 °C

Specifications: Conductivity
Range: 0 to 7 S/m (0 to 70 mS/cm)
Resolution: 0.00001 S/m
Accuracy: 0.0003 S/m

Specifications: Salinity
Resolution: 0.0002 PSU
Accuracy: 0.005 PSU

Instrument Type: Sea-Bird Electronics SBE 4 Conductivity Meter

Description: A Wein Bridge oscillator to generate a frequency output in response to changes in conductivity

Location: Water sampled at Laboratory seawater intake
Latitude 38° 18' 59.46" N
Longitude 123° 04' 15.34" W

Installed: 15 April 1988 - 2001

Specifications: Conductivity
Range: 0 to 7 S/m (0 to 70 mS/cm)
Resolution: 0.00001 S/m
Accuracy: 0.003 S/m

Specifications: Salinity
Resolution: 0.0002 PSU
Accuracy: 0.005 PSU

Instrument Type: Platinum Resistance Thermometer

Resolution: 0.01 °C

Accuracy: 0.05 °C

Special Note: Until December 1989, the sensor was positioned in a large sump. Water flowed frequently but not continuously through the sensor. During periods of non-flow, salinity readings may have been more varialble than during periods of flow.